Lead pellets are used conventionally in hunting activities. Density is the characteristic which confers lead pellet with its excellent mechanical and ballistic properties. This characteristic is what makes it very difficult to obtain new materials for the manufacture of pellets suitable for said hunting activities.
However, the high toxicity of lead, which signifies a steady impairment of the environment, especially in wetlands, as well as the poisoning of a great number of animal species, has created the need to develop multiple solutions to palliate this serious problem.
One of the substitutes for lead is steel and, in fact, ammunition is marketed based on this material. However it has serious drawbacks among which are its low density and its greater hardness with respect to lead, which necessarily implies a larger quantity of explosive, limiting, thereby, the weapon that can be used.
In the American patent U.S. Pat. No. 4,949,644 the development is described of bismuth shot pellets. Said material has a density which is higher than that of steel but less than that of lead. Together with this problem, bismuth is a very brittle material, (mechanical property) which results in the fracture and disintegration of the pellet on impact.
In the American patents U.S. Pat. Nos. 5,264,022, 5,527,376 and 5,713,981 the development is described of shot pellets containing a binary alloy of iron and tungsten in different proportions (with a percentage of tungsten of 30-46%, of 40-60%, or of 30-65%). The main drawback of this material is its great hardness, which results in damage to the barrel of the weapon every time a shot is fired.
In the American patent U.S. Pat. No. 4,949,645 the development is described of pellets formed by tungsten and a powdered polymer (polyethylene or silicone rubber, for example). The problem with this material resides in that the projectile has no penetration because the kinetic energy is absorbed and dissipated in its own deformation.
In the American patent U.S. Pat. No. 6,149,705, the development is described of pellets comprising a core of tungsten carbide powder, which can also contain elements like tungsten or tantalum, coated with metals such as aluminium, bismuth, copper, tin or zinc. However, said ammunition has the drawback of over-hardness of the tungsten carbide core for which reason, on striking the objective of the hunt, it produces a perforation of the animal with egress of the ammunition.
In the document GB 2211920, the development is described of pellets consisting of zinc-aluminium or zinc-tin alloys, with possible additions of other metals like copper, magnesium, silicon, alkaline or alkaline-earth metals. Said pellets, however, have a low density with respect to that of lead, which can result in having to change the weapon.
In the document GB 2327113 A, the development is described of pellets consisting of a tin-bismuth alloy, preferably in the proportion of the eutectic point (45% Bi and 55% Sn), which also has drawbacks regarding its density and hardness.
In the patent U.S. Pat. No. 5,877,437 a procedure is described for obtaining projectiles from a composite material which comprises a metal matrix and metal particles. This type of material presents problems on impact.
In the patent WO01/59399 a procedure is defined for obtaining bullets and projectiles based on a material which comprises a conglomerate of metal and/or alloy particles which are compacted by a powered-metal system. The main drawback of this method resides in the characteristics of the type of material which imply the need to use high melting temperatures and pressures to be able to mould and obtain the final projectiles and bullets.
In the patent U.S. Pat. No. 6,536,352, a procedure is described for obtaining bullets from a material which comprises a matrix of metal particles bonded by a metal of low melting point to obtaining a powdered-metal product. The characteristics of this material require the use of high compacting pressures, for shaping and obtaining of the end product.
In the patent EP1457578 an ecological ammunition is described formed by a material of the powdered-metal type which comprises spherical particles of tungsten absorbed in a tin matrix and a method of production of said materials based on the application of pressures below 250 MPa. The employment of said pressures signifies a high additional expense.
However, in spite of the current developments, there continues to exist in the state of the art, the need to provide new alternative materials to lead for manufacturing ecological ammunition intended for hunting activities. Said materials must have an optimum density proximate to that of lead as well as ballistic and mechanical properties similar to those currently available with lead in order, on one hand, to prevent the impairment of the environment and, on the other, avoid modification to the design of the current cartridges and the explosive which is used for lead pellets.
Within these possibilities, are found materials of the ODS (oxide dispersion strengthened or particle dispersion) type, where particles with different degrees of oxidation are introduced in a metal alloy matrix, in such a way that they reduce the interfacial energy between particles and matrix. Thus, the unit maintains its mechanical characteristics, and its deformability without disintegrating on impact. This means they have advantages over composite materials, like that of the Patent U.S. Pat. No. 5,877,437, with regard to impact.
On the other hand, there are presently several types of fishing weights on the market, although that which is used most frequently and, is therefore the most common, is the lead weight. In contact with water lead gradually releases certain quantities of toxins into the medium as a function of the concentration or the levels of nitrates, chlorines and oxygen which the water contains.
Bacteria and toxins build up in the contaminated sediments degrading the quality of the water which is home to crabs, oysters, shrimps, shellfish and all types of fish, making them unfit for human consumption.
As an alternative to the use of lead, weights are to be found based on tin and bismuth, among others.
In the Canadian patent CA 2380704, reference is made to the manufacture of fishing weights based on tin alloys, plus other metals in smaller proportions like silver, copper, antimony, zinc, nickel, which alloys are not corrosive when exposed to seawater, and therefore do not contaminate the environment.
In the European patent EP 1154026, use is made of elements composed of tin-tungsten as substitutes for lead.
In the American patent US 2004/0055205, reference is made to the production of fishing jigs, the base material of which is tungsten carbide in the greater part in addition to other minority elements like cobalt, titanium carbide, tantalum or niobium carbide and traces of vanadium carbide, chromium carbide and nickel.
In the American patent U.S. Pat. No. 6,325,136, reference is made to the production of fishing weights from alloys based on bismuth in a proportion by weight of more than 48% and tin.
In the American patent U.S. Pat. No. 5,946,849, reference is made to the production of fishing jigs using bismuth alloys as base material with a percentage of bismuth by weight which varies between 50-98% and small additions of tin, antimony and zinc or mixtures of these.
Surprisingly, the present inventors have discovered a new ecological material of the ODS type, with particle dispersion, with a density which allows it to replace lead in the whole range of ballistic and mechanical properties, but without its toxic effects. The ammunition fabricated from this material has good properties relative to the range and the transmission of kinetic energy on impact thanks to its optimum deformability, thereby overcoming the drawbacks of the alternative materials to lead being used at the present time.
Said material is based on a metal alloy matrix in which strengthening particles are dispersed, the metal matrix consisting of an alloy of zinc and bismuth, of zinc and aluminium, of tin and bismuth or of tin and zinc, and optionally other materials of low melting temperature, and the strengthening particles being tungsten or ferro tungsten particles; it being possible also to reinforce the matrix with particles of tungsten or ferro tungsten oxides or carbides, or any compound of these.
The composition of this new material contributes to increasing the density of the alloy without affecting its mechanical properties of hardness, malleability, deformability, inertia, etc., and also provides it with ecological properties which permit its employment in different applications without contaminating the environment.
Thus, this material finds application in other such activities as the manufacture of fishhooks for game fishing, of inertial counterweights in automobiles, of X-rays and ionising radiation screens, of golf sticks, as well as in water pipes and plumbing fittings and in electrical and magnetic applications, overcoming the drawbacks arising from the use of lead.